System and method for prosthetic fitting and balancing in joints

ABSTRACT

A system and method for prosthesis fitting in joints comprising an artificial condyle and a spacer which cooperates with the condyle to form an artificial joint. The spacer embedded with at least one sensor which is responsive to a force generated between the condyle and the spacer. The artificial joint is adapted to move between a flexed position and an extended position defining a range of motion. The sensor is responsive to the force and generates an output representative of that force. The output is transmitted, either wirelessly or other, to a processor which utilizes an analysis program to display a representation of the forces applied. A practitioner utilizing the displayed analysis may intraoperatively determine the adjustments and balancing required within the artificial joint. The system may also utilize a ligament tension sensor which generates generates data representative of tension on a ligament of the artificial joint, and a joint angle sensor responsive to the range of motion of the artificial joint. The processor may be adapted to store the outputted sensor data to provide the practitioner with statistically relevant historical data.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a non-provisional application claimingpriority from Provisional Application Serial No. 60/365,678, filed Mar.19, 2002.

FIELD OF THE INVENTION

[0002] The present invention relates to joint replacement and, moreparticularly, to a system and method for prosthesis fitting andbalancing in joints.

BACKGROUND OF THE INVENTION

[0003] Some medical conditions can result in the degeneration of a humanjoint, causing a patient to consider and ultimately undergo jointreplacement surgery. While joint replacement surgery is well known inthe art, the decision to undergo such a procedure may be a difficultone, as the long-term success of the surgery oftentimes relies upon theskill of the surgeon and may involve a long, difficult recovery process.

[0004] The materials used in a joint replacement surgery are designed toenable the joint to move just like a normal joint. The prosthesis isgenerally composed of a metal piece that fits closely into and bears ona corresponding plastic component. The plastic component is typicallysupported on another metal piece. Several metals are typically used,including stainless steel, alloys of cobalt and chrome, and titanium,while the plastic material is typically constructed of a durable andwear resistant polyethylene. Plastic bone cement may be used to anchorthe prosthesis into the bone, however, the prosthesis may be implantedwithout cement when the prosthesis and the bone are designed to fit andlock together directly.

[0005] To undergo the operation, the patient is given an anestheticwhile the surgeon replaces the damaged parts of the joint. For example,in knee replacement surgery, the damaged ends of the bones (i.e., thefemur and the tibia) and the cartilage are replaced with metal andplastic surfaces that are shaped to restore knee movement and function.In another example, to replace a hip joint, the damaged ball (the upperend of the femur) is replaced by a metal ball attached to a metal stemfitted into the femur, and a plastic socket is implanted into thepelvis, replacing the damaged socket. Although hip and knee replacementsare the most common, joint replacement can be performed on other joints,including the ankle, foot, shoulder, elbow and fingers.

[0006] As with all major surgical procedures, complications can occur.Some of the most common complications are typically thrombophlebitis,infection, stiffness, and loosening. While thrombophlebitis (i.e., veininflammation related to a blood clot) and infection are oftentimestreated medically, stiffness and loosening may require additionalsurgeries. One technique utilized to reduce the likelihood of stiffnessand loosening relies upon the skill of the surgeon to align and balancethe replacement joint along with ligaments and soft tissue duringsurgery.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a block diagram of a computer system illustrating anexample environment of use for the disclosed system;

[0008]FIG. 2 is a block diagram of a joint prosthesis fitting andbalancing system;

[0009]FIG. 3 is a front perspective view of an embodiment of aprosthesis fitted within a human knee;

[0010]FIG. 4 is a top perspective view of an embodiment of a spacer ofthe system of FIG. 2;

[0011]FIG. 5 is a bottom perspective view of the spacer of FIG. 4;

[0012]FIG. 6 is a side perspective view of an embodiment of a portion ofthe system of FIG. 2;

[0013]FIG. 7 is a front perspective view of an embodiment of a portionof the system of FIG. 2;

[0014]FIG. 8 is a side view of an embodiment of a prosthesis fittedwithin a human knee, wherein the knee is bent at zero degrees;

[0015]FIG. 8A is a graph plotting pressure readings in the prosthesis ofFIG. 8;

[0016]FIG. 9 is a side view of an embodiment of a prosthesis fittedwithin a human knee, wherein the knee is bent at thirty degrees;

[0017]FIG. 9A is a graph plotting pressure readings in the prosthesis ofFIG. 9;

[0018]FIG. 10 is a side view of an embodiment of a prosthesis fittedwithin a human knee, wherein the knee is bent at sixty degrees;

[0019]FIG. 10A is a graph plotting pressure readings in the prosthesisof FIG. 10;

[0020]FIG. 11 is a graph plotting pressure readings as a function ofjoint angle of a prosthesis of FIG. 2 during flexion of the prosthesis;

[0021]FIG. 12 is a graph plotting pressure readings as a function ofjoint angle of a prosthesis of FIG. 2 during extension of theprosthesis;

[0022]FIG. 13 is a topographical pressure graph plotting pressurereadings against a three dimensional rendering of an embodiment of aspacer of FIG. 2;

[0023]FIG. 14 is a topographical pressure graph plotting pressurereadings against a three dimensional rendering of an embodiment of aspacer of FIG. 2;

[0024]FIG. 15 is a topographical pressure graph plotting pressurereadings against a three dimensional rendering of an embodiment of aspacer of FIG. 2;

[0025]FIG. 16 is a top perspective view of an embodiment of a jig whichmay be used in conjunction with the system of FIG. 2;

[0026]FIG. 17 is a diagrammatic view of a wireless graphical hand-heldoutput display in accordance with one possible form of the presentinvention; and

[0027]FIG. 18 is a block diagram of an exemplary data collectionmodeling/analysis display scheme.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] A block diagram of an example computer system 10 is illustratedin FIG. 1. The computer system 10 may be a personal computer (PC) or anyother computing device capable of executing a software program. In anexample, the computer system 10 includes a main processing unit 12powered by a power supply 13. The main processing unit 12 illustrated inFIG. 1 includes one or more processors 14 electrically coupled by asystem interconnect 16 to one or more memory device(s) 18 and one ormore interface circuits 20. In an example, the system interconnect 16 isan address/data bus. Of course, a person of ordinary skill in the artwill readily appreciate that interconnects other than busses may be usedto connect the processor(s) 14 to the memory device(s) 18. For example,one or more dedicated lines and/or a crossbar may be used to connect theprocessor(s) 14 to the memory device(s) 18.

[0029] The processor(s) 14 may include any type of well knownmicroprocessor, such as a microprocessor from the Intel Pentium™ familyof microprocessors. The illustrated main memory device 18 includesrandom access memory such as, for example, dynamic random access memory(DRAM), or static random access memory (SRAM), but may also includenon-volatile memory. In an example, the memory device(s) 18 store asoftware program which is executed by one or more of the processors(s)14 in a well known manner.

[0030] The interface circuit(s) 20 are implemented using any type ofwell known interface standard, such as an Ethernet interface and/or aUniversal Serial Bus (USB) interface. In the illustrated example, one ormore input devices 22 are connected to the interface circuits 20 forentering data and commands into the main processing unit 12. Forexample, an input device 22 may be a keyboard, mouse, touch screen,track pad, track ball, isopoint, and/or a voice recognition system.

[0031] In the illustrated example, one or more displays, printers,speakers, and/or other output devices 24 are also connected to the mainprocessing unit 12 via one or more of the interface circuits 20. Thedisplay 24 may be a cathode ray tube (CRT), a liquid crystal display(LCD), or any other type of display, such as a hand-held display 500 asshown in FIG. 17. The display 24 may generate visual indications of datagenerated during operation of the main processing unit 12. For example,the visual indications may include prompts for human operator input,calculated values, detected data, etc.

[0032] The illustrated computer system 10 also includes one or morestorage devices 26. For example, the computer system 10 may include oneor more hard drives, a compact disk (CD) drive, a digital versatile diskdrive (DVD), and/or other computer media input/output (I/0) devices.

[0033] The illustrated computer system 10 may also exchange data withother devices via a connection to a network 118. The network connectionmay be any type of network connection, such as an Ethernet connection,digital subscriber line (DSL), telephone line, coaxial cable, etc. Thenetwork 118 may be any type of network, such as the Internet, atelephone network, a cable network, and/or a wireless network.

[0034] An example system for prosthesis fitting and balancing in jointsis illustrated in FIG. 2. In one embodiment, the system includes aprosthesis 30, a joint angle sensor 36, a ligament tension sensor 38, ananalysis program 40, the main unit 12, the one or more storage devices26, and the display 24. As will be described in detail below, theartificial joint may comprise a femoral component 32, a tibial tray 58,and a spacer 34 with one or more imbedded sensors 35. Any or all of thesensors 35, 36, 38 may be implemented by conventional sensor technology,including commercially available pressure sensors, tension sensors, andangle sensors. Furthermore, any or all of the storage device 26, and theanalysis program 40 may be implemented by conventional electroniccircuitry, firmware, and/or by a microprocessor executing softwareinstructions in a well known manner. However, in the illustratedexample, the analysis program 40 is implemented by software stored onthe memory 18 and executed by the processor 14, while the storage device26 may be implemented by database server software stored on the memory18, and executed by the processor 14 to physically store data on a harddrive. In addition, a person of ordinary skill in the art will readilyappreciate that certain modules in the apparatus shown in FIG. 2 may becombined or divided according to customary design constraints. Stillfurther, one or more of the modules may be located external to the mainprocessing unit 12.

[0035] Turning to FIG. 3, there is shown an example of the prosthesis 30as used in conjunction with the replacement of a human knee 50. Ingeneral, the human knee 50 comprises a femur 52, a patella 53, a tibia54, a plurality of ligaments (not shown), and a plurality of muscles(not shown). The prosthesis 30 generally comprises two parts, thefemoral component 32 and a tibial component 56. Additionally, the tibialcomponent 56 is typically made up of two parts, the metal tibial tray 58that is attached directly to the tibia 54 and the spacer 34 thatprovides the bearing surface. It will be understood that the while inthe disclosed embodiment the tibial component 56 is comprised ofseparate components, the spacer 34 and the metal tibial tray 58 may beintegrally formed. The materials used in a joint replacement surgery aredesigned to enable the joint to mimic the behavior or a normal kneejoint.

[0036] In the illustrated embodiment, the femoral component 32 is ametal piece, shaped similar to the end of the femur and fitting closelyinto a corresponding plastic spacer 34. Several metals are typicallyused, including stainless steel, alloys of cobalt and chrome, andtitanium, while the plastic material is typically constructed of adurable and wear resistant polyethylene. Other suitable materials maynow exist or may be developed in the future. Plastic bone cement may beused to anchor the prosthesis 30 into the bones 52, 54, however, theprosthesis 30 may be implanted without cement when the prosthesis 30 andthe bones 52, 54 are designed to fit and lock together directly. Acemented prosthesis 30 is held in place by a type of epoxy cement thatattaches the metal to the bones 52, 54. An uncemented prosthesis 30 hasa fine mesh of holes on the surface that allows the bones 52, 54 to growinto the mesh and attach the prosthesis 30 to the bones 52, 54.

[0037] Referring now to FIGS. 4 and 5, there is illustrated an examplespacer 34 which may be used in conjunction with an embodiment of thesystem of FIG. 2. The spacer 34 includes a pair of opposed faces 60, 62and an elongated side edge 64. The face 60 comprises a pair of condylerecesses 68, 66, shaped to closely match or otherwise accommodate theshaped end of the femoral component 32. The face 60 may also comprise anextension 70 which may slidably engage a groove 71 in the femoralcomponent 32 and prevent lateral movement between the spacer 34 and thefemoral component 32, while allowing the two pieces to rotate relativeto each other in a predefined range of motion similar to a biologicalknee, for example, between zero degrees (0°), i.e., extension, andninety degrees (90°), i.e., flexion. The contact between the femoralcomponent 32 and the spacer 34 will produce deformations in the twosurfaces in contact, which may be measured by the sensors 35 embedded inthe spacer 34. The sensed deformation may cause an output to be createdby the sensors 35.

[0038] The opposite face 62 includes an elevated face 72. The elevatedface 72 and the face 62 cooperate to form a snap-fit connection with thetibial tray 58 as is well known in the art. It will be noted thatconnection between the tibial tray 58 and the spacer 34 may varyaccording to known design variations. For instance, the elevated face 72and the face 62 may be substantially coplanar and may be cemented ontothe tibial tray 58.

[0039] In the illustrated embodiment of FIG. 5, the elevated face 72 isillustrated with a plurality of recesses 74. The recesses 74 are milledin the face 72 of the polyethylene and have a cross section sized toaccept sensors 35, thereby enabling the sensors 35 embedded in thespacer 34. Since the sensors 35 are responsive to the deformation of thespacer 34, the depth of the recesses 74 may be chosen to minimize theimpact on the deformation characteristics of the spacer 34, as well asto ensure an accurate reading based on the sensitivity of the sensor 35.

[0040] For example, in the illustrated embodiment, the recesses 74 havea cross section of appropriately dimensioned to accept a strain sensormarketed by Omega Engineering, Inc., of Stanford, CT. In one embodiment,the recesses are arranged in an array and include a bar-shaped microminiature strain gage (sensor 35) of approximate dimension 1 mm ×0.5 mm0.15 mm. The strain gage is responsive to the deformation of curvaturewith a maximum strain of 3000μ. Furthermore, the strain gage may providedata in a real-time, or near real-time fashion, allowing forintraoperative analysis of the data. A person of ordinary skill in theart will readily appreciate that other sensors may be used to sense thedeformation of the spacer 34. For example, a single sensor, or an arrayof sensors may be used to sense the deformation of the spacer 34.

[0041] Once the sensor 35 is placed in the recesses 74, the recesses maybe filled with a plug of the same, or similar, material as the spacer34, to further minimize the impact on the deformation characteristics ofthe spacer 34. The recess plug may be, for example, glued in place, orheld by an interference fit. Of course, a person of ordinary skill inthe art will readily appreciate that any number of recesses 74 andsensors 35 may be utilized. Moreover, the dimensions of the recesses mayvary greatly, depending upon the characteristics of the spacer 34, thesensor 35, and/or the desired sensitivity. Still further, it will beappreciated that the sensors 35 may be embedded within the spacer 34utilizing any known or yet to be developed manufacturing method,including direct insertion during the molding process, as well asinsertion utilizing a transverse cut in the spacer 34.

[0042] The spacer 34 illustrated in FIG. 5 includes a plurality ofsensors 35 electrically coupled by a system interconnect (not shown) toone or more transceiver device(s) 76. In the example, the systeminterconnect is a plurality of wires (not shown) transversely carriedthrough the spacer 34 to the transceiver device(s) 76. Of course, aperson of ordinary skill in the art will readily appreciate thatinterconnects other than wires may be used to connect the sensors 35 tothe transceiver devices(s) 76. For example, one or more wirelessconnections may be used to connect the sensors 76 to the transceiverdevice(s) 76. In the illustrated embodiment, the transceiver device(s)76 is embedded within another recess 77 within the elevated face 72 ofthe spacer 34, however, it will be understood that the transceiver maybe located in any location, including external to the spacer 34.

[0043] In one embodiment, the transceiver device(s) 76 is a selfpowered, 5 channel input transceiver having approximate dimensions of1.46 cm ×3.05 cm ×0.65 cm. The transceiver has a sample rate of 150samples per second and is powered by a 3.1 volt minimum, 7 volt maximum,13.8 DC battery. Additionally, the transceiver may contain a memory forstoring sensor data. In operation, the transceiver device 76 is adaptedto receive, as an input, multiple sensor outputs created by each of thesensors 35 in response to the deformation of the spacer 34. Thetransceiver device 76 is further adapted to convert the multiple sensorinputs to a serial data stream and transmit the data stream, via wiredor wireless connection, to the main unit 12. The transceiver devices 76is preferably a single battery powered transceiver capable of wirelesstransmission, however, it may be any type of transceiver known or yet tobe developed, such as a magnetically powered transceiver. Furthermore,it will be appreciated by one of ordinary skill in the art that thetransceiver device(s) 76 and the sensors 35 may be combined or dividedaccording to customary design constraints. Still further, the spacer 34with embedded sensors 35 may be designed to be substantially permanentlyattached to the tibial tray 58, i.e., bioengineered to remain in theprosthesis 30 after surgery, or it may be temporarily attached to thetibial tray 58, i.e., to be used only during the actual replacementsurgery to gather data and replaced by a substantially permanent spacer.In the disclosed example, this is aided by the fact that the sensors 35,etc. are fully encapsulated in the spacer 34.

[0044] Referring now to FIG. 6 and 7, there is illustrated a human kneeexposed for surgery with the prosthesis 30 and sensors 35, 36, 38 inplace. Specifically, the femoral component 32 is attached to the femur52, and the tibial component 56 is attached to the tibia 54. The spacer34 and embedded sensors 35 are in place between the femoral component 32and the tibial tray 58. In the illustrated embodiment, a plurality ofligament tension sensors 38 are attached to external knee ligaments,such as, for example, the medial cruciate ligament and the lateralcruciate ligament. Additionally, the joint angle sensor 36 may beattached to the surface of the human knee 50.

[0045] The ligament tension sensors 38 may be any commercially availabletension sensors such as one marketed by Omega Engineering, Inc., ofStanford, Conn. The ligament tension sensor 38 is responsive to thetension of the ligament to which it is attached, and is adapted toproduce an output in response to the sensed tension. The ligamenttension sensor 38 may also comprise a transceiver (not shown) similar tothe above-described transceiver device 76. The data output from theligament tension sensor 38 may thereby be transmitted to the main unit12.

[0046] The joint angle sensor 36 may be any commercially available anglesensor such as one marketed by Omega Engineering, Inc., of Stanford,Conn. The joint angle sensor 36 is responsive to the range of motion ofthe prosthesis 30, and is adapted to produce an output representative ofthe joint angle. The joint angle sensor 36 may also comprise atransceiver (not shown) similar to the above-described transceiverdevice 76. The data output from the joint angle sensor 36 may thereby betransmitted to the main unit 12.

[0047] As will be appreciate by one of ordinary skill in the art, thesensors 35, 36, 38 may be used in any number of combinations, dependingupon the desired data collection strategy. For example, a practitionermay only be interested in the pressure between the spacer 34 and thefemoral component 32 when the prosthesis is fully extended, and maytherefore, only utilize the sensor 35 and the joint angle sensor 36.

[0048] Once all the desired sensors 35, 36, 38 are in place, it may bedesirable to partially close the incision to evaluate the prosthesis 30range of motion during flexion and extension. The surgeon may then flexthe prosthesis 30 through its normal range of motion. The outputs fromthe sensors 35, 36, 38 are transmitted to the main unit 12, wherein theymay be captured by the analysis program 40. In one embodiment, theanalysis program 40 may be, for example, LabVIEW™data acquisitionsoftware marketed by National Instruments Corp., of Austin, Tex. andcommercially available.

[0049] The analysis program 40 may display the data in a variety offormats on the display(s) 24, as will be described below. The analysisprogram 40 may be adapted to transmit the acquired data to the databaseserver software stored on the memory 18, and executed by the processor14 to physically store data on a hard drive.

[0050] In one embodiment, as shown by FIGS. 8 through 10A, the sensor35, 38 measurements are captured by the analysis program 40 anddisplayed as a pressure distribution graph. Specifically, referring toFIGS. 8 and 8A, the analysis program 40 displays a three dimensionalpressure distribution graph 100, in pounds per square in (lb/in²) whenthe prosthesis 30 is in the zero degree (0°) extension position(illustrated by FIG. 8). As described in detail above, the pressuredistribution graph is representative of the sensed pressure on thespacer 34 by the femoral component 32. The illustrative pressuredistribution graph 100 displays six regions of pressure sensor readings,namely an anterior 102, 104, a middle 106, 108, and a posterior region110, 112, duplicated on both the medial and lateral portions of thespacer 32 respectively. It will be understood that while six regions102, 104, 106, 108, 110, 112 are displayed, each region may be comprisedof any number of individual sensor readings, including multiple readingsper region.

[0051] Referring to FIGS.9 and 9A, and FIGS.10 and 10A, the analysisprogram 40 displays a three dimensional pressure distribution graph 120,140 in pounds per square in (lb/in²) when the prosthesis 30 is in thethirty degree (30°) extension position (illustrated by FIG. 9), and whenthe prosthesis 30 is in the sixty degree (60°) extension position(illustrated by FIG. 10). As described in above, the illustrativepressure distribution graphs 120, 140 display six regions of pressuresensor readings, namely an anterior 102, 104, a middle 106, 108, and aposterior region 110, 112, duplicated on both the medial and lateralportions of the spacer 32 respectively.

[0052] The graphical pressure distribution graphs may allow thephysician to adjust their surgical or medical procedures by examiningthe pressure within the prosthesis 30 at certain angles. For example,the physician may recognize, either by experience or knowledge of designconstraints, that the medial anterior pressure region 102 of FIG. 8A isslightly elevated and may adjust the prosthesis 30 accordingly.Additionally, the analysis program 40 may provide the physician with thetension readings provided by the ligament tension sensors 38 (not shown)to aid the physician in determining whether, based upon the knowledgeand skill of the surgeon, the ligaments should be adjusted.

[0053] In yet another embodiment, the analysis program 40 may be adaptedto compare the acquired data to the data stored by the database serversoftware on the hard drive. For example, upon the collection of a numberof trials of empirical data, the stored data may be statisticallyanalyzed (either by the analysis program 40, or another externalprogram) to form suggested pre-determined pressure criteria, i.e., upperand lower limits, to aid the physician in recognizing potential elevatedpressure readings. The suggested predetermined pressure criteria maydefine statistically sound thresholds and allowable limits under certainconditions, and may be constantly adjusted as more information becomesavailable in the database.

[0054] In yet another embodiment, as shown by FIGS. 11 and 12, thesensor 35, 38 measurements are captured by the analysis program 40 anddisplayed as a pressure graph as a function of joint angle.Specifically, referring to FIGS. 11 and 12, the analysis program 40displays a two dimensional pressure graph 200, 220 in pounds per squareinch (lb/in²) when the prosthesis 30 is moving in the flexion range ofmotion (FIG. 11) and when the prosthesis 30 is moving in the extensionrange of motion (FIG. 12). Again, as described in detail above, thepressure distribution graph is representative of the sensed pressure onthe spacer 34 by the femoral component 32.

[0055]FIG. 11 illustrates a graph plotting the six sensor regions 102104, 106, 108, 110, 112 marked by their respective reference numeralsversus joint angle, wherein the prosthesis 30 is moving in flexion. FIG.12 illustrates a graph plotting the six sensor regions 102 104, 106,108, 110, 112 marked by their respective reference numerals versus jointangle, wherein the prosthesis 30 is moving in extension. As the graphsof FIG. 11 and 12 show, the pressure on each region varies according tojoint angle, providing the physician with a graphical understanding ofthe mechanics of the prosthesis 30 and allowing the physician to adjusttheir surgical or medical procedures by examining the pressure withinthe prosthesis 30 over the full range of motion.

[0056] It will be understood that the sensor 35, 36, 38 measurementscaptured by the analysis program 40 and may be displayed in any numberof various ways, including, raw data dumps, and as graphs, similar tothose disclosed above. For example, in another embodiment (not shown),the analysis program 40 may display a pressure graph as a function ofligament tension. It will be appreciated, however, that the examplegraphs above are merely illustrative, and are no way limiting.

[0057] In still another embodiment, the outputs from the sensors 35, 36,38 may be transmitted to the main unit 12, wherein they may be capturedby another embodiment of the analysis program 40 which may be, forexample, a finite element analysis program(“FEA”program). An example ofan FEA program is the ANSYS Finite Element Analysis software programmarketed by ANSYS Inc. located in Canonsburg, Pa., and commerciallyavailable.

[0058] The FEA analysis program 40 is flexible, and may display the datain a variety of formats on the display(s) 24. In one embodiment, asshown by FIGS. 13 through 15, the sensor 35, 38 measurements arecaptured by the FEA analysis program 40 and displayed as both a pressuredistribution graph, and as a pressure topography graph. Specifically,referring to FIG. 13, the FEA analysis program 40 displays a threedimensional pressure topography graph 300, in kilopascal (kPa) when theprosthesis 30 is in the zero degree (0°) position. Similar to the otherembodiments, for example a pressure distribution graph 310, and asdescribed in detail above, the pressure topography graph 300 isrepresentative of the sensed pressure on the spacer 34 by the femoralcomponent 32 at a specific angle. Unlike the pressure distribution graph310, however, the illustrative pressure topography graph 300 displaysthe pressure in relationship to the modeled spacer 34, allowing thepractitioner to identify the location of the pressure points in spatialrelation to the spacer 34 used.

[0059] Referring to FIGS. 14 and 15, the analysis program 40 displays athree dimensional pressure topography graph 320, 340 in kilopascal (kPa)when the prosthesis 30 is in the forty degree (40°) position(illustrated by FIG. 14), and when the prosthesis 30 is in the ninetydegree (90°) position (illustrated by FIG. 15). As described in above,the illustrative pressure topography graphs 320, 340 displays pressurein relationship to the modeled spacer 34, as opposed to the six regionpressure distribution graphs 330, 350.

[0060] Referring now to FIG. 16, there is illustrated a jig 400 whichmay be used in the operative environment of FIGS. 6 and 7, oralternatively, in a testing environment, such as cadaver testing, or thelike. The jig 400 is arranged to control the flexion of the prosthesis30 in the intra operative environment is such a way that a number ofvariables may be controlled. For example, the jig may control, forinstance, the rate of flexion and extension, the total range of motion,and the axis of motion, etc., in such a manner that the user mayexperience consistent and reproducible results when testing variousaspects of the prosthesis 30.

[0061] It will be noted that while the above description relates to anembodiment of a human a prosthetic, it will be readily understood thatthe principles of the present invention may be applied to any type ofreplacement joint, as well as any living organism. For example, thesensors 35 of the present embodiment may be utilized to replace a hipjoint, or other joint, including the ankle, foot, shoulder, elbow andfingers. For instance, in hip joint replacement, the damaged ball (theupper end of the femur) is replaced by a metal ball attached to a metalstem fitted into the femur, and a plastic socket is implanted into thepelvis, replacing the damaged socket. The sensors 35 may be embeddedwithin the plastic socket (or other location) to provide thepractitioner with data related to the contact between the metal stem andthe socket.

[0062] It will be further understood that the main unit 12 may bearranged to receive input from an MRI, CAT scan, X-ray, and/or otherdiagnostic device to feed the analysis program 40 with that input. Theanalysis program 40 may then convert that input to a model of thepatient's knee. The model may reduce or eliminate the need forconventional intermedullar rods conventionally used to determine thespecific of the tibial and femoral cut down, such as location, angle,etc. One example of these data collection, finite element analysisand/or joint modeling steps, along with there respective graphicaloutputs or displays is shown in FIG. 18.

[0063] A system and method according to the disclosed example may serveto improve longevity and function of Total Knee Arthroplasty (TKA). Theaccurate balancing of the forces acting on the joint in a total kneearthroplasty results in proper component placement and proper tensioningof the ligamentous structures that cross the knee joint. When a kneearthroplasty is properly balanced, stresses are evenly distributed inthe articulating components through a full range of motion. Functionallypoor ligament balance, which can create instability causing acutesubluxation or dislocation of the total knee components, may be reducedor eliminated. On the other hand, tight ligaments can produce stiffnesslimiting or precluding knee motion. More subtle discrepancies inligament balancing create abnormally high peak stresses in the articularcomponents and at the bone prosthesis interface causing catastrophicfailure of polyethylene tibial components or mechanical loosening at thebone cement interface. Additionally, undue stresses can increasecomponent wear, which is deleterious because the wear particles arephagocytized by macrophages initiating an inflammatory cascade thatstimulates osteoclast activity. This causes osteolysis with bone lossand degradation of the bone implant interface and eventual loosening.

[0064] In accordance with the disclosed example, the necessaryexperimental and analytical tools to quantify and standardize balancingof the knee joint during TKA may be developed. Additional data may becollected from cadaver total knee arthroplasty experiments in order tocorrelate stress measurements with abnormalities of ligamentous balanceand component position.

[0065] Using the system disclosed herein, as the knee is flexed througha complete range of motion the pressures may be collected in real timeor in near real time. While the knee is flexed tension will be measuredin the structures bridging the joint to measure the effect of increasedtension on the stress values. Data may also be obtained on the effect ofcomponent malposition on the stresses across the knee.

[0066] The data obtained may be used to create a mathematical model forknee arthroplasty. For example, a clinical advisory board of orthopedicsurgeons may be established to define possible criteria needed toachieve acceptable conformity in a balanced knee. A rough paradigm maybe developed to aid in guiding the surgeon in interpretation of stressdata obtained during knee arthroplasty. Stress data may be obtainedduring total knee implantation intraoperatively using a wireless sensorydevice. The paradigm may be tested and fine tuned so that stress datacan guide the surgeon in achieving proper balance when performing TKA.

[0067] The disclosed system may further aid in investigating the forcerequirements from the collateral segments and how they influence thepressure/contact between the femoral and tibial component duringflexion-extension. The effects of pressure on the wear on thepolyethylene component of the biomechanics of the knee may be readilystudied, threshold limits of pressure values deemed acceptable tobalance the knee after TKA may be. developed. An analytical dynamicalmodel of the knee will used to analyze the experimental data.

[0068] A dynamic model of the knee depicting all the intricate detailssuch as contact in the presence of active forces, patella, collateralligaments, attachment points, bone density, design characteristic of theprosthesis, interface between bone and femoral-tibial components, may bedeveloped using known methodologies.

[0069] In this phase of the study pressure profiles will be createdcorresponding to specific increments of misalignment. This synthesiswill validate the information with the concurrent experiment that hasimplemented the sensor technology. An advisory board will be set upwhere clinicians and surgeons will set up threshold for contact pressurein the TKA. Based on precalibrated values of experimental study, thesurgeon can then do proper ligament release or component exchange tobring the values within acceptable limits. Eventually, this will betaken as guidelines which will allow a precision fit in the operatingroom without any reliance on the experience of the surgeon. Effectivelythis study will lead in achieving a higher level of joint mobilityperformance in arthritic patient. Ultimately, not only a better trackingmechanism of wear and performance of the TKA will be developed but alsothe clinician's performance during the surgery will be evaluated throughthe quantitative feedback he receives.

[0070] Based on the results a special jig 400 will be designed toimmobilize the femur while allow free motion of the tibia and quadricepsmechanism. The components will then be implanted and the knee will beplaced in the special jig 400. A computerized winch will pull on thequadriceps tendon duplicating the force and the direction of thequadriceps muscle. The rectus femoris and vastus intermedius will betied together and loaded with a 30-N weight, the rectus medialis will beloaded with 25-N weight and the vastus lateralis will be loaded with20-N. Finally, a high precision potentiometer (shape sensor) will beused to measure the joint angle. The knee will then be flexed andextended from 0 to 9° degrees. A distribution of contact pressure willbe recorded as a function of angle. The leg will also be outfitted withan angle sensor on the side of the knee in order to measure joint angle.The sensors will allow readings of stress and tension in real time asthe knee is brought through the complete flexion cycle. The effect ofeach particular reefing on peak joint stresses will be measured andabnormal tension in the shortened ligament will be correlated with peakjoint stresses through the flexion cycle. Finally the components will beplaced in abnormal positions of valgus, varus, flexion and extension andthe pressures again measured through the flexion cycle.

[0071] A Sample Experimental Procedure:

[0072] An experimental knee replacement procedure was performed on amock human knee 50. Once the experimental knee replacement surgery wasperformed, a traditional spacer was removed and replaced with one thathad six pressure sensors 35. the sensors 35 and the main unit 12 werecoupled through the use of wires. The knee 50 was stitched with thewires running through the wound. The femur 52 was immobilized with thejig 400 and the quadriceps were loaded. The joint angle sensors 36 wereput in place. The knee 50 was then extended and flexed through thenormal range of motion many times. The rate pf flexion was approximately20 degrees per second. Caution was taken in order not to apply externalvarus or valgus stress. The cycle of extension and flexion was repeatedmany times and recordings were averaged.

[0073] A finite element model was created by scanning the actual spacer34 with a laser micrometer and importing the geometry into a computerfile. Using Autocad, a three dimensional file was refined and thenexported in to an ANSYS compatible format. The current ANSYS spacermodel has over 23,000 elements, which have 20nodes each and atetrahedral shape. On the surface of each condyle 66, 68, twelve hundredand fifty nine (1259) nodes resided. These nodes are responsible for theapplication of all pressure and forces to the model while the bottomsurface is constrained to have zero displacement. The spacer model wasdesigned so that data could be inputted into the model easily using datafrom the output sensors 35. ANSYS was then used to generate thenecessary plots of stress —both principal stresses and von-Mises stressplots of the deformation of the tibia component were be displayed asfunction of time variant pressure do to tibiofemoral contact.

[0074] The contact pressures at each sensor 35 was displayed for kneeextension and flexion. The joint angle range of motion varied fromroughly ninety degree (90°) to zero degrees (0°). During knee extension,very small contact forces were recorded while the knee was betweenninety degrees (90°) and fifty degrees(50°). For example, one sensorshowed activity between fifty degrees (50°) and twenety five degrees(25°) with a maximum of 40 psi at approximately 35°. Another sensorrecorded a maximum at sixteen degrees (16°) with pressure of 110 psi.During flexion, contact pressures were recorded with slightly largermagnitudes. For example one sensor, which recorded no more than 3-psiduring extension, recorded 10-psi at around seventy five degrees (75°)during flexion. Similarly, another sensor which recorded a maximum atthirty five degrees (35°) during extension, recorded a maximum while attwenty five degrees (25°) during flexion.

[0075] As a result, it may be concluded that for this experiment, forceson the medial and lateral condyle were not balanced in phase ormagnitude. This would suggest a varus-valgus unstable knee. The highpressure recorded at the extended end of the graph suggested a jointthat is too tight.

[0076] Numerous modifications and alternative embodiments of theinvention will be apparent to those skilled in the art in view of theforgoing description. Accordingly, this description is to be construedas illustrative only and is for the purpose of teaching those skilled inthe art the best mode of carrying out the invention. The details of thesystem may be varied substantially without departing from the spirit ofthe invention, and the exclusive use of all modifications which arewithin the scope of any subsequent claims is reserved.

What is claimed is:
 1. A system for prosthesis fitting in jointscomprising: an artificial condyle; a spacer, the spacer cooperating withthe condyle to form an artificial joint, the spacer adapted to support aforce from the condyle, the artificial joint being adapted to movebetween a flexed position and an extended position defining a range ofmotion; a sensor embedded within the spacer, the sensor being responsiveto the force, wherein the sensor generates an output representative ofthe force; a processor having a memory, the processor being operativelycoupled to the sensor, the processor memory being adapted to store theoutput representative of the force on the spacer by the condyle; acomputer analysis program stored on the processor memory, the computeranalysis program being adapted to analyze the output representative ofthe force on the spacer.
 2. A system for prosthesis fitting in joints asdefined in claim 1, wherein the artificial joint is moveable through arange of motion, and wherein the sensor is arranged to provide aplurality of outputs each corresponding to a plurality of angles of theartificial joint within the range of motion.
 3. A system for prosthesisfitting in joints as defined in claim 1, wherein the sensor is a straingage, the strain gage being adapted to generate a voltage in response tothe forces on the spacer.
 4. A system for prosthesis fitting in jointsas defined in claim 1, wherein the sensor comprises an array ofindividual sensors embedded in the spacer.
 5. A system for prosthesisfitting in joints as defined in claim 4, wherein each of the individualsensors is embedded within a recess formed in the spacer.
 6. A systemfor prosthesis fitting in joints as defined in claim 1, wherein thespacer comprises a transceiver having a memory, the transceiver beingoperatively coupled to the sensor.
 7. A system for prosthesis fitting injoints as defined in claim 6, wherein the transceiver is arranged towirelessly communicate with the processor.
 8. A system for prosthesisfitting in joints as defined in claim 1, further comprising a database,wherein the database is adapted to store the output representative ofthe force on the spacer.
 9. A system for prosthesis fitting in joints asdefined in claim 1, wherein the computer analysis program is a finiteelement analysis program.
 10. A system for prosthesis fitting in jointsas defined in claim 9, wherein the finite element analysis program isadapted to output a pressure topography graph.
 11. A system forprosthesis fitting in joints as defined in claim 10, further comprisinga display, wherein finite element analysis program is adapted to outputthe pressure topography graph on display.
 12. A system for prosthesisfitting in joints as defined in claim 1, further comprising a ligamenttension sensor, the tension sensor adapted for placement on a ligamentand arranged to produce an output indicative of a tensile force appliedto the ligament.
 13. A system for prosthesis fitting in joints asdefined in claim 12, further comprising a display, wherein the datarepresentative of the force is illustrated as a function of the tensileforce applied to the ligament.
 14. A system for prosthesis fitting injoints as defined in claim 2, further comprising a joint angle sensor,the joint angle sensor being responsive to the range of motion of theartificial joint, wherein the sensor generates data representative of anangle of the artificial joint.
 15. A system for prosthesis fitting injoints as defined in claim 13, further comprising a display, wherein thedata representative of the force is illustrated as a function of thejoint angle.
 16. A system for prosthesis fitting in joints as defined inclaim 2, including a jig arranged to move the artificial joint throughthe range of motion.
 17. A system for prosthesis fitting in joints asdefined in claim 15, wherein the jig is arranged to move the artificialjoint at a controlled rate of flexion.
 18. A system for prosthesisfitting in joints as defined in claim 15, wherein the jig includes anangle sensor.
 19. A system for prosthesis fitting in joints as definedin claim 15, wherein the jig is arranged to control at least one of avarus angle and a valgus angle.
 20. A system for prosthesis fitting injoints as defined in claim 15, wherein the jig is arranged to apply acontrolled load to the artificial joint.
 21. A system for prosthesisfitting in joints as defined in claim 1, further comprising: a ligamenttension sensor, the tension sensor being responsive to the range ofmotion of the artificial joint, wherein the sensor generates datarepresentative of tension on a ligament of the joint; a joint anglesensor, the joint angle sensor being responsive to the range of motionof the artificial joint, wherein the sensor generates datarepresentative of an angle of the artificial joint; and wherein the datarepresentative of the force is illustrated as a function of the jointangle and as a function of the ligament tension.
 22. A system forprosthesis fitting in joint arthroplasty comprising: an artificialcondyle; a spacer, the spacer cooperating with the condyle to form anartificial joint, the spacer adapted to support a force from thecondyle, the artificial joint being adapted to move between a flexedposition and an extended position defining a range of motion; a sensorembedded within the spacer, the sensor being responsive to the force,wherein the sensor generates an output representative of the force; aligament tension sensor, the tension sensor being responsive to therange of motion of the artificial joint, wherein the sensor generatesdata representative of tension on a ligament of the artificial joint; ajoint angle sensor, the joint angle sensor being responsive to the rangeof motion of the artificial joint, wherein the sensor generates datarepresentative of an angle of the artificial joint; a processor having amemory, the processor being operatively coupled to the sensor, theprocessor memory being adapted to store the output representative of theforce on the spacer by the condyle; a computer analysis program storedon the processor memory, the computer analysis program being adapted tointraoperatively analyze the output representative of the force on thespacer, the data representative of an angle of the artificial joint, andthe data representative of tension on a ligament of the artificialjoint.
 23. A system of claim 22, wherein the artificial joint ismoveable through a range of motion, and wherein the sensor is arrangedto provide a plurality of outputs each corresponding to a plurality ofangles of the artificial joint within the range of motion.
 24. A systemof claim 23, wherein each of the individual sensors is embedded within arecess formed in the spacer.
 25. A system of claim 22, wherein thespacer comprises a transceiver having a memory, the transceiver beingoperatively coupled to the sensor and wherein the transceiver isarranged to wirelessly communicate with the processor.
 26. A system ofclaim 22, further comprising a database, wherein the database is adaptedto store the output representative of the force on the spacer, the datarepresentative of an angle of the artificial joint, and the datarepresentative of tension on a ligament of the artificial joint
 27. Asystem of claim 22, wherein the computer analysis program is a finiteelement analysis program.
 28. A system of claim 27, wherein the finiteelement analysis program is adapted to output a pressure topographygraph and wherein the computer analysis program is adapted to receiveand output load threshold limits to the pressure topography graph.
 29. Aspacer for cooperating with an artificial condyle to form an artificialjoint, the spacer adapted to support a force from the condyle, thespacer comprising: a sensor embedded within the spacer, the sensor beingresponsive to the force, wherein the sensor generates an outputrepresentative of the force.
 30. A spacer as defined in claim 29,wherein the artificial joint is moveable through a range of motion, andwherein the sensor is arranged to provide a plurality of outputs eachcorresponding to a plurality of angles of the artificial joint withinthe range of motion.
 31. A spacer as defined in claim 30, wherein eachof the individual sensors is embedded within a recess formed in thespacer.
 32. A spacer as defined in claim 29, further comprising atransceiver, the transceiver being operatively coupled to the sensor andwherein the transceiver is arranged to wirelessly communicate.
 33. Aspacer as defined in claim 32, further comprising a power supply, thepower supply being electrically coupled to the transceiver.
 34. A devicefor intraoperative use in balancing joint forces and verifying theplacement of the tibial component in total knee arthroplasty comprising:a spacer defining an enclosure, the spacer sized to engage a top portionof the tibial component; a sensor array embedded in the spacer, thesensor array arranged to create an output indicative of the forces onthe spacer; a wireless transceiver embedded in the spacer and arrangedto forward the output to a processor; the processor arranged to analyzethe output and create a pressure distribution graph indicative of theforces on the spacer; thereby assisting a surgeon in performingselective soft tissue release or component positioning in connectionwith surgical implantation of an orthopaedic knee prosthesis.
 35. Thedevice of claim 34, including a signal conditioning and signaltransmitting circuit capable of sending the output through wirelesscommunication to a receiver operatively connected to the processor. 36.The device of claim 34, wherein the spacer includes a power supplydisposed inside a tibial post of tibial component, and wherein the powersupply is insulated to thereby prevent patient injury from leakage ormicroshock.
 37. A method for prosthesis fitting in joints comprising:providing an artificial condyle; providing a spacer, the spacercooperating with the condyle to form an artificial joint, the spaceradapted to support a force from the condyle, the artificial joint beingadapted to move between a flexed position and an extended positiondefining a range of motion; embedding a sensor within the spacer, thesensor being responsive to the force, wherein the sensor generates anoutput representative of the force; storing the output representative ofthe force on the spacer by the condyle in a processor having a memory,the processor being operatively coupled to the sensor; analyzing theoutput representative of the force on the spacer in a computer analysisprogram stored on the processor memory.
 38. A method for prosthesisfitting in joints as defined in claim 37, wherein the artificial jointis moveable through a range of motion, and further comprising arrangingthe sensor to provide a plurality of outputs each corresponding to aplurality of angles of the artificial joint within the range of motion.39. A method for prosthesis fitting in joints as defined in claim 37,further comprising arranging the sensor as an array of individualsensors embedded in the spacer.
 40. A method for prosthesis fitting injoints as defined in claim 39, further comprising embedding each of theindividual sensors within a recess formed in the spacer.
 41. A methodfor prosthesis fitting in joints as defined in claim 37, furthercomprising transmitting the output representative of the force via atransceiver having a memory, the transceiver being operatively coupledto the sensor.
 42. A method for prosthesis fitting in joints as definedin claim 41, further comprising embedding the transceiver within thespacer
 43. A method for prosthesis fitting in joints as defined in claim41, further comprising transmitting the output representative of theforce by wirelessly communicating with the processor.
 44. A method forprosthesis fitting in joints as defined in claim 37, further comprisingstoring the output representative of the force on the spacer in adatabase.
 45. A method for prosthesis fitting in joints as defined inclaim 37, further comprising displaying the analysis of the outputrepresentative of the force on the spacer on a display.
 46. A method forprosthesis fitting in joints as defined in claim 45, further comprisingdisplaying a pressure topography graph.
 47. A method for prosthesisfitting in joints as defined in claim 38, further comprising providing aligament tension sensor, the tension sensor adapted for placement on aligament and arranged to produce an output indicative of a tensile forceapplied to the ligament.
 48. A method for prosthesis fitting in jointsas defined in claim 47, further comprising displaying the datarepresentative of the force as a function of the tensile force appliedto the ligament.
 49. A method for prosthesis fitting in joints asdefined in claim 38, further comprising providing a joint angle sensor,the joint angle sensor being responsive to the range of motion of theartificial joint to generate data representative of an angle of theartificial joint.
 50. A method for prosthesis fitting in joints asdefined in claim 49, further comprising displaying the datarepresentative of the force as a function of the joint angle.
 51. Amethod for prosthesis fitting in joints as defined in claim 38, furthercomprising moving the artificial joint through the range of motion
 52. Amethod for prosthesis fitting in joints as defined in claim 51, furthercomprising controlling the range of motion of the artificial joint witha jig.
 53. A method for prosthesis fitting in joints as defined in claim5 1, further comprising controlling the rate of flexion of theartificial joint with a jig.
 54. A method for prosthesis fitting injoints as defined in claim 5 1, further comprising controlling the rateof extension of the artificial joint with a jig.
 55. A method forprosthesis fitting in joints as defined in claim 5 1, further comprisingcontrolling at least one of a vargus angle and a valgus angle of theartificial joint with a jig.
 56. A method for prosthesis fitting injoints as defined in claim 51, further comprising controlling a load tothe artificial joint with a jig.